Personal identification system

ABSTRACT

A personal identification system, which uses a vein pattern of a finger, optimizes the amount of light of a light source based on a captured finger image and emphasizes the vein pattern during image processing for identification.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a technology for identifying aperson using a living body, and more particularly to a technology foridentifying a person using a finger vein pattern.

[0002] Today, the typical personal identification technology isfingerprint identification. However, the problem is that other person'sfingerprint is easily obtained, for example, a criminal's fingerprint istaken in the scene of a crime, and therefore a finger-print may beforged. This problem leads to the development of personal identificationtechnologies other than fingerprint identification. For example,JP-A-7-21373, laid-open Jan. 24, 1995, discloses a personalidentification technology thorough the use of a finger blood vesselpattern, and JP-A-10-295674, laid-open Nov. 10, 1998, discloses apersonal identification technology through the use of a vein pattern onthe back of a hand. These technologies shine a light on a finger or onthe back of a hand, capture the reflected light or transmitted light,extract the blood vessel pattern from the captured image, and comparethe captured blood vessel pattern with the previously-registered bloodvessel pattern to identify a person.

SUMMARY OF THE INVENTION

[0003] However, there are some problems in implementing a personalidentification system that uses finger vein patterns.

[0004] One of the problems is the reproducibility of a captured image.Although a conventional personal identification system has positioningparts such as a pin or a grasping bar for stabilizing the imagingregion, an error in the imaging region is unavoidable, for example, whena finger is rotated or moved in the plane or when a finger is rotated onits major axis. Therefore, it is difficult to completely match aregistered vein pattern with a vein pattern obtained at identificationtime, with the result that the performance of identification is reduced.In particular, on a fully-non-contact system on which the finger is notput on something for fixing, a registered vein pattern and a capturedvein pattern may differ largely and this difference further reduces theperformance of identification.

[0005] Another problem is a light source. A conventional personalidentification system has no function to adjust the amount of light fromthe light source. This generates several image-quality problems such asa blurred outline of a captured image, a lack in sharpness, and a lowcontrast. These problems require a complex image-processing algorithmfor correction and sometimes result in the low performance ofidentification

[0006] According to one aspect of the present invention, means describedbelow is used for improving reproducibility. First means is an algorithmfor correcting an error detected during image processing that isexecuted for matching an imaged finger blood vessel pattern with aregistered pattern. This correction prevents the performance ofidentification from being degraded.

[0007] Second means is a three-dimensional imaging of a living body fromvarious angles using a plurality of imaging devices. Even if aregistered vein pattern was imaged from only one direction, that is, theregistered pattern is two-dimensional data, the finger may be placedfreely when imaged for identification. Therefore, even if there is anerror in the imaging region, one of the plurality of images may beselected for use in matching. This prevents the performance ofidentification from being degraded. It is also possible to registerthree-dimensional vein patterns as patterns to be registered by imagingthe vein pattern from a plurality of directions. In this case, one ofthe plurality of registered vein patterns is selected for matching. Thisalso prevents the performance of identification from being degraded evenif there is an error in the imaging region.

[0008] Combining the first means with the second means further increasesthe performance of identification

[0009] A light source with means for optimizing the amount of light atimaging time is used as the light source. This configuration optimizesthe amount of light from the light source to make the quality of acaptured image best.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a diagram showing an example of the configuration of asystem that captures the blood vessel image of a living body using anoptical method.

[0011]FIG. 2 is an external view of a personal identification system inan embodiment of the present invention.

[0012]FIGS. 3A and 3B are diagrams showing a low-contact fingerpositioning method.

[0013]FIG. 4 is a diagram showing a light source composed of arrangedlight-emitting devices.

[0014]FIG. 5 is a diagram showing a three-dimensional imaging methodusing the three-dimensional arrangement of imaging devices.

[0015]FIG. 6 is a flowchart showing a procedure for capturing a fingerimage-in the embodiment of the present invention.

[0016]FIG. 7 is a diagram showing the positioning of fingers atidentification time when air is jetted.

[0017]FIG. 8 is a diagram showing an identification device using air jetused in an embodiment of the present invention.

[0018]FIGS. 9A, 9B, and 9C are diagrams showing the sterilization methodused on a contact identification device.

[0019]FIG. 10 is a diagram showing the overview of processing fromfinger image capturing to identification in the embodiment of thepresent invention.

[0020]FIG. 11 is a diagram showing a procedure executed from fingerimage capturing to identification in the embodiment of the presentinvention.

[0021] FIGS. 12A-12G are diagrams showing a first example of thecreation of an image to be registered and an image to be authenticatedin the embodiment of the present invention.

[0022]FIGS. 13A, 13B, and 13C are diagrams showing a second example ofthe creation of an image to be registered and an image to beauthenticated in the present invention of the present invention.

[0023]FIG. 14 is a diagram showing a first example of the method fornormalizing identification processing results in the embodiment of thepresent invention.

[0024]FIG. 15 is a diagram showing a second example of the method fornormalizing identification processing results in the embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] (First Embodiment)

[0026]FIG. 1 is an example of the basic configuration of a personalidentification system. FIG. 2 shows an embodiment of a personalidentification system according to the present invention. The systemcomprises a light source unit 101 that shines a light on a finger, animaging unit 103 that captures the image of a finger, and an imagingprocessing unit 104 that processes captured image data. As the lightsource, a semiconductor light source, such as an LED (Light EmittingDiode), is usually used because of its responsiveness andcontrollability. A CCD camera is used as the imaging unit. A personalcomputer is conveniently used as the imaging processing unit 104 thatcaptures an image into the computer via the inter-face such as an imagecapture board. The imaging processing unit 104 performs processingnecessary for identifying a captured image. Numeral 201 indicates awindow through which a light from the light source transmits. Anautomatic shutter may be provided on the window to prevent a light frombeing leaked from the surrounding part of the finger to ensure accuracyin image processing. An automatic shutter may also be providedseparately between the light source and the finger. Numeral 202 indicatepins that fix the imaging region. These pins are optional. If there isno pin, the system is a fully non-contact system. The imaging unit 103captures a vein pattern image formed by the light transmitted throughthe finger.

[0027] As a vein pattern for use in personal identification, it is morepreferable to use the vein pattern of a palm-side finger than to use thevein pattern of a back-side finger. This is because the vein pattern ofthe back-side finger, which is always exposed externally, is more likelyto be stolen. In this embodiment, the system always images the veinpattern of the palm-side finger.

[0028]FIG. 3A is a diagram showing the fingers exposed to the lightsource unit 101 shown in FIG. 1, as viewed from the front. FIG. 3B is adiagram showing the positional relation among light-emitting devices 301constituting the light source, positioning pins 205, a finger 302, andan imaging device 303, as viewed from the tip of the finger. Numeral 304indicates a transmitted light.

[0029] A plurality of light-emitting devices, which make up the lightsource, are arranged according to the shape of a finger, as shown inFIG. 4. Although near-infrared, high-intensity light-emitting diodes(LEDs) are used as the light source, a laser beam may also be used.Numerals 401, 402, 405, and 406 are the front views of many types oflight source. Numeral 401 indicates the shape of a light source made upof a plurality of conventional mold-type near infrared light-emittingdiodes (near-infrared LEDs) arranged linearly. Because each of theplurality of light-emitting devices indicated by numeral 401 is round,the brightness of the light source is uneven. To solve this problem, theround edges of the plurality of mold-type LEDs are removed to form thelight source in the shape indicated by numeral 402. Numeral 407 is thefront view, and numeral 408 is the cross sectional view, of an LED whoseedges have been removed. The shaded areas indicated by numeral 407 arethe areas that are removed. The view indicated by numeral 403, a crosssectional view of the light source indicated by numeral 402, indicatesthe light source formed by arranging a plurality of LEDs each in theshape indicated by numerals 407 and 408. This arrangement eliminatesunevenness in the source light and increases the packing density and thelight source intensity. Numeral 405 is an example of a light source madeup of a plurality of chip-type LEDs arranged in the plane. In any case,a plurality of LEDs are arranged to detect the location of a fingerbased on the image monitored by the imaging unit, and the light sourceelements to be turned on are selected to form a light source accordingto the thickness and the length of a finger.

[0030]FIG. 6 shows the procedure for capturing a finger image. As thelight source, a weak light is kept on at all times (601). The systemchecks if a finger is exposed to the weak light (602) and, if a fingeris present, detects the location of the finger (603.). The presence andthe location of the finger are detected based on the pixel value data ofthe monitor image. Based on the location data of the detected finger,the system decides which elements of the light source to be turned on(604). In addition, the system acquires the pixel data of the monitorimage (605) to optimize the amount of light to be supplied from thelight source.

[0031] The procedure for optimizing the amount of light is as follows.When human being's finger or toe is imaged, the light transmissionfactor is highest in joints. Therefore, the system detects a joint fromthe light intensity profile of a finger in the major axis in the imagedata and uses the maximum intensity value as the intensity value (B) ofthe joint. This value is compared with the reference value (A) ofintensity that is previously set. If A−B<0, the light source issubjected to a feedback to reduce the input current to the light source.If A−B>0, the current input to the light source is increased. WhenA−B=0, the system ends the adjustment of light intensity, captures theimage, and starts image processing. Performing this processing for eachlight-emitting device optimizes not only the amount of light but alsothe area of the light source. In this case, the light source with theconfiguration composed of chip-type, small LEDs arranged in the plane,such as the one indicated by numeral 405 in FIG. 4, is best. Thisconfiguration is effective for shining a light on a finger whosethickness and length vary greatly.

[0032] The method described above adjusts the light source output tooptimize the light intensity. Alternatively, adjusting the time duringwhich the light stays on may also optimize the light intensity.

[0033] To optimize the amount of light, it is required that the joint beidentified. Two sample procedures for identifying the joint will bedescribed. In one procedure, a portion with a relatively highlight-intensity value is detected in the image profile of a blood vesselpattern of a finger, imaged through the use of transmitted light, toidentify the joint of the finger. Then, a feedback is effected such thatno pixel reaches the intensity value of 255 in the 8-bit dynamic range.In another procedure, an image to which a spatial low-pass filter isapplied in the major axis direction of a finger in the captured image isevaluated, and the amount of light of the light source striking thejoint is adjusted. Any of the procedures described above forms a lightsource with a spatial intensity distribution.

[0034] The above-described configuration for automatically adjusting theamount of light is suitable for capturing a high-contrast blood vesselimage. Adjusting the amount of light significantly increases the qualityof a blood vessel image, allowing person identification throughimage-to-image operation of captured images to be performed smoothly.

[0035] With a previously registered finger blood vessel as the template,personal identification operation is performed through the calculationof correlation to find a similarity between the blood vessel patternimage of a finger imaged at authentication time and the template. Thecalculation of correlation is a monotone increasing calculation in whichan output value increases in proportion to the degree of matching oftwo-dimensional array elements. Most typically, a two-dimensionalconvolution calculation (formula 1) is used. $\begin{matrix}{{{z( {{k1},{k2}} )} = {\sum\limits^{m}{\sum\limits^{n}{{x( {i,j} )}\quad {y( {{{k1} + 1 - i},{{k2} + 1 - j}} )}}}}}( {{{k1} = 1},2,{{\cdots \quad m} + n - 1},{{k2} = 1},2,{{\cdots \quad m} + n - 1}} )} & ( {{Formula}\quad 1} )\end{matrix}$

[0036] One to ten fingers, usually up to all fingers and toes may beregistered. Depending upon the required security level, the number offingers to be compared may be increased. In some cases, a non-fingerblood vessel image may also be used with a finger image.

[0037]FIG. 10 is a block diagram showing the personal identificationprocedure executed based on the image of a detected finger. Personalidentification processing is divided roughly into two: registrationprocessing and authentication processing. Registration processing,blocks 1000-1001, is processing in which a database 100 is created basedon the images registered at registration time. Authenticationprocessing, blocks 1002-1005, is processing in which a person isaccepted or rejected based on the calculation of correlation between animage that is input for identification and a registered image.

[0038] During registration processing, the image detecting meanscaptures a person's finger image to be registered (block 1000). At thesame time, registration image creation processing, which will bedescribed later, is performed to create a finger-vein emphasized imageand the created image is registered (block 1001). On the other hand,during authentication processing, the personal information receivingmeans receives a person's ID (block 1002) and, at the same time, theregistered image corresponding to the received ID is selected from thedatabase (block 1003). In addition, the image detecting means capturesan identfee's image to be authenticated (block 1004) and, at the sametime, authentication image creation processing, which is similar toregistration image creation processing and will be described later, isperformed to create a blood vein emphasized image (block 1005), and thecalculation of correlation between the captured image and the registeredimage is executed.

[0039] Then, the result of the calculation of correlation is evaluated,and the authentication result indicating whether or not he/she is anidentical person is output. Most typically, a two-dimensionalconvolution calculation is used as the calculation of correlation. Inthis case, even if the finger is translated in the image plane, thedistribution obtained as a result of the two-dimensional convolutionoperation is also translated with no change in size and shape.Therefore, the evaluation of similarity between these two imagesautomatically corrects errors generated by the translation in the imageplane. In addition, taking advantage of the fact that the convolutionoperation between two data units is equivalent to-the inverse Fouriertransformation of the product of the Fourier-transformed data units,two-dimensional Fast Fourier Transform (hereinafter called FFT) may beused to speed up the calculation of correlation.

[0040]FIG. 11 is a block diagram showing the image operation procedurewhen FFT is used to speed up the calculation of correlation. Finger-edgeextraction and image-rotation processing (block 1101) is performed forthe captured image to be registered or for the captured image to beauthenticated. During this processing, the finger edge is extracted and,based on the extracted edge, the image is rotated so that the fingerinclination becomes constant. Even when the physical location of thefinger is inadequate, this processing corrects an error in the rotationin the image plane and precisely locates the finger in the image space.This processing, combined with the characteristics of thetwo-dimensional calculation of correlation described above, correctserrors associated with finger movement operations (both translation androtation) in the image place and correctly locates the finger in theimage space.

[0041] The image to be registered and the image to be authenticated, forwhich finger-edge extraction and image-rotation processing has beenperformed, are each converted to a finger-vein emphasized image (block1102), and the two-dimensional FFT operation is executed for theconverted result (block 1103). The result generated for the former imageis registered. The result generated for the latter image is multipliedby the registered image selected based on the received ID (block 1104).Then, two-dimensional fast inverse Fourier transformation (Inverse FFT,hereinafter called IFFT) is performed for the result (block 1105) toproduce the correlation distribution of the registered image and theimage to be authenticated. As described above, the same image processingis performed for blocks 1101 to 1103 during registration image creationprocessing (block 1001) and during authentication image creationprocessing (block 1005).

[0042] The personal identification system may include a light sourcewhich shines a light on the imaging region of a living body, an imagingunit which detects a transmitted light from the imaging region to imagethe living body, and an imaging processing unit which extracts the bloodvessel pattern of the living body from the image converted by theimaging unit and compares the pattern with a previously-registered bloodvessel pattern, wherein the image processing unit may comprises meansfor correcting an error between the registered blood vessel pattern andthe imaged blood vessel pattern.

[0043]FIG. 12A is a block diagram describing in detail an example of theblood vessel emphasizing processing procedure. FIGS. 12B-12D are thegeneral views of a finger image generated by each processing procedure.

[0044] An input image is divided roughly into a finger 120, an edge 121,and a surrounding part 122. In general, the image also includes variousnoises 123 that must be removed. In FIG. 12A, blocks (1201)-(1203)execute the procedure for extracting the edge of a finger, blocks(1204)-(1206) execute the procedure for extracting an imagecorresponding to the background (back-trend) that is the part where nofinger vein pattern is present, and blocks (1207)-(1211) execute theprocedure for removing the back-trend from the original image to extractonly the necessary vein pattern.

[0045] In response to a captured finger image (block 1200), a high-cutfilter filters out small components such as noises 123 (block 1201) andemphasizes only relatively large components such as the edge. Then, theprocedure executes directional differentiation (block 1202) to give anedge-enhanced image (FIG. 12C).

[0046] As shown in the image in FIG. 12C, the edge 121 in the edgeenhanced image is enhanced and has a large pixel value. Based on thepixel value, the procedure performs edge detection processing to obtainonly the location information on the edge 121 (block 1203). Then, basedon the location information on the detected edge, the procedure producesan image (FIG. 12D) generated by clipping out only the finger 120 fromthe original image shown in FIG. 12B (block 1204).

[0047] In the image shown in FIG. 12D, the average of the pixel valuesoutside the finger is made equal to the average of the pixel valuesinside the finger. Without this averaging operation, the finger edgecomponent emphasized by finger the edge emphasizing processing wouldaffect the operation, preventing personal identification operationthrough the vein pattern from being performed properly.

[0048] When the average of the pixel values inside the finger is shiftedto 0, the pixel value of 0 is inserted into the surrounding part 122 ofthe image shown in FIG. 12D. Then, after an image (FIG. 12E) is createdby extraporation of the values of the surrounding part 122 of the imageshown in FIG. 12D in the vertical direction by use of the values of theedge 121 (block 1205), only the large component, that is, theback-trend, is extracted with a high-cut filter (block 1206). In theblock 1205, extrapolation is performed to prevent the high-cut filter inthe block 1206 from unintentionally emphasizing the pixel value near theedge 121.

[0049] Next, after creating a difference image between the originalimage (FIG. 12B) and the back-trend image (block 1208), the clipped-outimage (FIG. 12F) of the difference image is obtained based on thedetected edge location. The difference corresponds to a part processedby a low-cut filter. This processing removes the back-trend componentgenerated by a light transmitted through muscles or fat tissue or bydiffused lights. Therefore, an image where only the blood vesselcomponent is emphasized, such as the one shown in FIG. 12F, is obtained.

[0050] Finally, according to the inclination of the finger obtained fromthe detected edge location, the image is rotated such that the finger isinclined at a fixed angle, typically, at an angle of 0 degree (FIG. 12G)(block 1209). This image is output as the image to be registered or asthe image to be authenticated (block 1210).

[0051]FIG. 15 is a block diagram showing the authentication procedurethat is executed after the image to be authenticated is obtained by theprocedure in FIG. 12. The calculation result of correlation between theregistered image and the image to be authenticated is normalized by theformula shown below (formula 2) (block 1503), followed by the extractionof the maximum value M of the distribution (block 1504).

Cab(x, y)/({square root}{square root over (Caa(x, y))}×{square root}{square root over (Cbb(x, y))})  (Formula 2)

[0052] where, Cab(x,y) is the correlation distribution of the registeredimage and the image to be authenticated. Caa(x,y) and Cbb(x,y) representa sum of squares of respective pixel data of a registered image and asum of squares of respective pixel data of an image to be authenticated,respectively.

[0053] If the calculated maximum correlation value M of the registeredimage and the image to be authenticated is larger than the threshold Mo,the identifee is regarded as valid and is accepted (block 1009). If thevalue M is less than the threshold Mo, the identifee is not regarded asvalid and is rejected (block 1010). The threshold Mo should bestatistically calculated in advance by entering sample images. When theaverage of pixel values inside the finger is shifted to the value of 0,the value of Mo ranges from 0.45 to 0.55. However, the value is notlimited to this range.

[0054] If a person is not acknowledged, he or she must re-enter data,such as finger image capture data, to make a re-authentication request apredetermined number of times. For example, a person who is successfullyacknowledged is allowed to access managed data or areas. On the otherhand, a person who is not acknowledged makes a re-authentication requesta predetermined number of times and, if the person is not yetacknowledged, access to the managed data or areas is rejected.

[0055] It is desirable that the personal information input means, whichis used to select a person's registered finger image from the database,not be a keyboard but a non-contact device. For example, personalinformation such as a name or a password, or a keyword that is knownonly to the person, may be input via voice or, alternatively, stored ona non-contact IC card. This type of input means makes it possible tobuild a personal identification system that takes advantage ofnon-contact features. This processing may be done independently by theCPU of the identification system or by an online system via computers.

[0056] An image to be authenticated is stored on a fixed mediumconnected to the authentication server, a medium containingsemiconductor memory, or a portable medium such as a floppy disk. Thismethod eliminates the need for keyboard operation on a banking ATM,solves the problems associated with a contact input device, and relievesa maintenance nuisance. The advantages described above make this methodsuitable for gaining access to personal information in an electronicgovernment or for authentication in online transactions.

[0057] (Second Embodiment)

[0058] In the first embodiment, a finger is imaged with one CCD camera.A finger may also be imaged with a plurality of CCD cameras duringauthentication or image capturing to increase the performance ofidentification.

[0059]FIG. 5 shows the arrangement of this embodiment where a pluralityof CCD cameras are used; that is, a light source 301, a finger 302, andCCD cameras (303-1-303-5) are arranged as shown. In this embodiment, aplurality of finger vein patterns are captured from a plurality ofdirections using a plurality of CCD cameras, and the pattern mostsimilar to the registered vein pattern is selected for authentication.Alternatively, a plurality of vein patterns to be registered arecaptured and saved as three-dimensional data and, from these patterns,the pattern most similar to the vein pattern to be authenticated isselected for authentication. This method is particularly effective forpreventing the performance of identification from being degraded whenthe finger is rotated in the major axis direction and, at the same time,effective for implementing a complete-non-contact device.

[0060] Not only a still image but also a moving image may be imaged.When imaging and registering a three-dimensional moving image, a fingeris rotated in the configuration, shown in FIG. 3B, which is composed ofthe light source LED (301), finger (302), and imaging device (303).Alternatively, as shown in FIG. 5, a plurality of CCD cameras may beused to capture an image from a plurality of points. A person isauthenticated either by a two-dimensional image imaged by the imagingunit in the configuration shown in FIGS:. 3A and 3B or by athree-dimensional image imaged by the imaging unit in the configurationshown in FIG. S.

[0061] The image is captured into the processing unit for use in imageoperation and authentication. Because the most similar vein pattern tobe registered or the most similar vein pattern to be authenticated isselected for authentication, this method is advantageous in that theperformance of identification is increased and the image operation loadis reduced.

[0062] (Third Embodiment)

[0063] FIGS. 13A-13C are block diagrams showing in detail one example ofblood vessel emphasizing processing (corresponds to blocks 1101-1103 inFIG. 11). When a finger image is received (block 1000 or 1004), edgedetection processing is performed to detect the location of the fingeredge (block 1300). Based on the detected edge location, image rotationprocessing is performed so that the image is rotated such that thefinger is inclined at a fixed angle, typically, at an angle of 0 degree(block 1301). Blood pattern emphasizing processing is performed for theobtained image (block 1302).

[0064] For example, blood pattern enhancement processing is performedusing a filter, such as the one shown in FIG. 13B, designed to removehigh-frequency components in the major axis direction of the finger, andlow-frequency components in the minor axis direction. Filtering may bedone either by the convolution operation (formula 1) in the real spaceor by the multiplication operation in the frequency domain. For theimage where the blood vessel pattern is enhanced, the average of thepixel values outside the finger is made equal to the average of thepixel values inside the finger, based on the edge location detected bythe edge detection processing (block 1300), as in FIGS. 12A-12G (block1303). When shifting the average of the pixel values inside the fingerto 0, the pixel values outside the edge are set to 0.

[0065] Two-dimensional FFT transform operation is performed for theobtained image (block 1103), squaring of respective pixel data of theobtained is performed (block 1304), and then two-dimensional IFFToperation is performed (block 1305). For the obtained result, theparameters for evaluation are calculated (block 1306). Because vesselsusually run in the major axis direction of the finger rather than in theminor axis direction, the difference in the blood vessel pattern is mostreflected in the peak shape in the minor axis direction of the finger inthe two-dimensional convolution operation result. Therefore, theparameters for evaluation are calculated, for example, using a kernelcomposed only of the elements in the minor-axis direction of the fingersuch as the one shown in FIG. 13C, to perform convolution operation inthe real space or multiplication in the frequency domain.

[0066] If the input image is an m×n matrix and the kernel is a p×1matrix, then the result of the calculation of parameters for evaluationis a (m+p−1)×n matrix. The maximum value Mx of the resulting matrix iscalculated for each of the registered image and the image to beauthenticated. Let the maximum value be M1 and M2, respectively. M1 isstored in the database (100).

[0067]FIG. 14 is a block diagram showing the authentication procedureexecuted after block 1007 when an image is processed according to theprocedure shown in FIG. 13A. Calculation of parameters for evaluation(block 1403) is executed for the result of the calculation ofcorrelation between the registered image and the image to beauthenticated. For the calculated maximum value M, normalizationoperation (block 1404) is performed according to the formula (formula 3)based on M1 and M2 described above.

M=M ₁₂/{square root}{square root over (M ₁ ×M ₂)}  (Formula 3)

[0068] If the calculated value MX of correlation between the registeredimage and the image to be authenticated is larger than the thresholdMxo, the identifee is regarded as valid and is accepted (block 1009). Ifthe value Mx is less than the threshold Mxo, the identifee is notregarded as valid and is rejected (block 1010). The threshold Mxo shouldbe statistically calculated in advance by entering sample images. Whenthe average of pixel values inside the finger is shifted to 0 asdescribed above, the value of Mxo ranges from 0.3 to 0.4 but is notlimited to this range.

[0069] (Fourth Embodiment)

[0070] Because a fully non-contact method is not always advantageous incost, processing time, and compactness, it is more practical for adevice, while still retaining the non-contact features described above,to have the minimum positioning parts required for fixing an imagingregion such as a finger or a hand. Note that more bacilli are present onthe palm of a hand of a human being than on the back. Therefore, even ona device on which the imaging region contacts the positioning parts, thepalm of the hand should not contact the device. The following describesan example.

[0071]FIG. 7 shows a finger positioning method using air jet instead ofthe pins in FIGS. 3A and 3B. Compressed air is jetted from the jet hole(FIG. 7(700), FIG. 8(800)). Numeral 802 indicates an air compressor anda control system, and numeral 801 indicates a compressed-air intake. InFIG. 8, an air jet from the air jet hole on the palm side of the handprevents the palm from contacting the device. At identification time, aperson places his or her hand naturally in the position where the airjet from the hole 700 in FIG. 7 does not blow strongly against thefingers.

[0072] An optical sensor, which measures the distance between the deviceand the palm to check to see if the height, from the device to the palm,is correct, is provided to control image capturing. If the height isincorrect, incorrect-height information is sent to the identifee.Because the palm does not contact any object as described above, thisembodiment reduces the possibility of bacillus contagion caused by anunspecified number of persons using the device. Therefore, it can besaid that the method in this embodiment in which the palm does notcontact any object is better than a method in which the palm contactsthe device.

[0073] Winding a palm-contact sheet (900) or sterilizing the sheet witha ultraviolet light source (901) or a disinfectant (902) allows even apalm-contact device to take advantage of the identification systemaccording to the present invention that keeps the device clean. For fullsterilization, an optical-catalyzed (titanic-oxide) coated sheet is usedas the palm-contact sheet (900) and a ultraviolet light is shown on thesheet. Including this type of sterilizer keeps the device clean.

[0074] The embodiments described above allow a reliable, secure, andeasy-to-use personal identification system to be built. That is, afamiliar, forgery-proof, highly-accurate personal identification systemmay be implemented while eliminating or minimizing maintenancemanagement work executed for preventing contagion caused by dirt on thedevice or for preventing errors in obtained data.

What is claimed is:
 1. A personal identification apparatus comprising: alight source which irradiates a finger; an imaging unit which captures atransmitted light from the finger; an image processing unit whichextracts a blood vessel pattern from a image captured with the imagingunit, and compares the blood vessel pattern with a registered bloodvessel pattern; and a fixing device which doesn't contact a surface fromwhich the transmitted light passed and contacts a part of the finger;wherein the light source comprises light-emitting elements arrangedaccording to the shape of the finger as the capture.
 2. The personalidentification apparatus according to claim 1; wherein thelight-emitting devices are arranged in the long direction of the finger.3. The personal identification apparatus according to claim 1; whereinthe light-emitting devices are arranged are near-infrared light emittingdiodes.
 4. The personal identification apparatus according to claim 1;wherein the light-emitting devices emit near-infrared laser beam.
 5. Thepersonal identification apparatus according to claim 1; wherein thelight-emitting devices are arranged planimetrically.
 6. The personalidentification apparatus according to claim 1; wherein thelight-emitting devices are arranged on the straight line.
 7. Thepersonal identification apparatus according to claim 1; furthercomprising: a memory which stores the registered blood vessel patterns;wherein image processing unit authenticates the validity of the userbased on comparing the extracted blood vessel patterns with theregistered blood vessel patterns stored in the memory.
 8. The personalidentification apparatus according to claim 3; wherein each contiguouspart of the near-infrared light emitting diodes are coherent each other.9. The personal identification apparatus according to claim 3; whereineach contiguous part of the near-infrared light emitting diodes has aflat surface configuration.
 10. The personal identification apparatusaccording to claim 1; wherein a light source irradiates a dorsum of thefinger.
 11. The personal identification apparatus according to claim 1;wherein the fixing device is a pin.
 12. The personal identificationapparatus according to claim 1; further comprising wherein the personalinformation input means for selecting the registered blood vesselpattern.
 13. The personal identification apparatus according to claim12; wherein the personal information input means is a voice input meansor a IC card or a keyboard.
 14. The personal identification apparatusaccording to claim 1; wherein the image processing unit compares theextracted blood vessel pattern with the registered blood vessel patternstored on a fixed medium connected to the authentication server ormedium containing semiconductor memory or a portable medium.
 15. Apersonal identification apparatus comprising: a light source whichirradiates a capturing part of a finger at a distance; an imaging unitwhich detects a transmitted light through the capturing part andcaptures the capturing part; an image processing unit which extractsblood vessel patterns from a image captured with the imaging unit, andcompares the blood vessel patterns with a pre-registered blood vesselpatterns; a fixing device which does'nt contact a surface from which thetransmitted light passed and contacts a part of the finger; wherein thelight source comprises light-emitting devices arranged according to theshape of the finger as the capture.